Atrial fibrillation (“AF”) is a form of cardiac arrhythmia. “Atrial” refers to the top two chambers of the heart known as the atria, where irregularity in AF occurs. The atria are designed to send blood efficiently and rhythmically into the ventricles by way of regular electrical signals. From there, blood is pumped to the rest of the body. In AF, the electrical signals are rapid, irregular and disorganized, and the heart may not pump as efficiently. Individuals with AF have an increased risk of stroke. Stroke occurs if a piece of a blood clot in the atria leaves the heart and becomes lodged in an artery in the brain.
Current AF treatment options are not perfect. A medical practitioner may use medication as a treatment option. Medication, however, only assists in the management of the symptoms. It is not a cure for AF. Medication can also present side effects that may be more dangerous than AF itself. Another treatment option is electrical cardioversion. In certain circumstances, electrical cardioversion may be used to restore normal heart rhythm with an electric shock, but this option often results in AF reoccurrence.
When medication is not successful, the medical practitioner may treat AF with ablation catheter therapy. In this procedure, a catheter with an ablation element is introduced through a blood vessel and directed to the atria in the heart muscle. The medical practitioner will localize a specific area of cardiac tissue having aberrant electrically conductive pathways and emitting or conducting erratic electrical impulses. The medical practitioner will then deliver a burst of radio frequency (RF) energy to destroy the tissue that triggers abnormal electrical signals or to block abnormal electrical pathways. In AF, it has been shown that the source of the electrical abnormality is at the opening of each of the four pulmonary veins that come off the left atrium. The medical practitioner therefore targets these openings for ablation catheter therapy.
While the ablation catheter therapy has become more widely adopted, it is not without its difficulties. In order to effectively treat AF with this procedure, accurate placement and line formation of the lesions (i.e., adjacent lesions without gaps) are critical. Specifically, the success of atrial fibrillation ablation is dependent upon the creation of lesions that adequately disrupt the tissue's electrical properties. Current techniques do not permit the medical practitioner (operator) to determine exactly where the lesions have been made and whether energy has been efficiently delivered. The medical practitioner relies primarily on changes in electrical signals, which are interpreted as signs of adequate ablation but frequently result in restoration of electrical function after the ablation, and induced edema thus restores. In sum, accurate placement and line formation of ablation lesions are tough to achieve because visualization is inadequate. Consequently, it is thus difficult to effectively treat cardiac arrhythmias such as AF with current ablation technologies and methods. Improved methods and systems are thus needed to determine where ablation lesions have been made and whether the lesions are likely to be long-standing.